In many industries, including the beverage industry, products are packaged in containers which are returned after use, washed and refilled. Typically refillable containers are made of glass which can be easily cleaned. These containers are washed and then inspected for the presence of foreign matter.
Glass containers have the disadvantages of being fragile and, in the larger volumes, of being relatively heavy. Accordingly, it is highly desirable to use plastic containers because they are less fragile and lighter than glass containers of the same volume. However, plastic materials tend to absorb a variety of organic compounds which may later be desorbed into the product thereby adversely affecting the quality of the product packed in the container. It has been found that the existing methods of inspection are inadequate to detect containers which may have absorbed contaminants.
Two kinds of foreign matter detecting devices, one for inspecting the body (barrel) of a bottle and the other for inspecting the bottom, are known in the art. In the former device, light is externally applied to the bottle while the bottle is being rotated, and light passed through the bottle is detected by a photoelectric element. The photoelectric element is employed to compare the quantity of transmission light obtained when a certain region of the bottle has a foreign matter to the quantity of transmission light obtained when the certain region has no foreign matter. Typically the entire body of the bottle is inspected for a foreign matter. Illustrative of the above described detection system are the devices described in U.S. Pat. No. 4,376,951 (Mar. 15, 1983, Miyazawa) which comprises a photoelectric conversion device having a number of light receiving elements; and a video signal processing device for successively subjecting to comparison and discrimination the detection signals of variable two adjacent points which are detected by the photoelectric conversion device, to determine whether or not the bottle has a foreign matter.
Detecting devices which measure the degree of transmission through a container have the disadvantage that they cannot detect the presence of many contaminants that may have been absorbed into the wall of the container because some contaminants do not affect the transmission of light through the container.
U.S. Pat. No. 4,551,627 (Nov. 5, 1985 Reich) discloses apparatus for inspecting residual liquid such as water, oil, and liquid soap in refillable beverage containers. The apparatus is intended to detect liquids such as oil, and liquid soap which may contaminate the containers. In the apparatus disclosed small quantities of liquid contaminant are detected and the containers containing such residues are removed from the refillable container process line. The method for detecting the contaminant comprises the steps of: measuring optical transmittances of a combination of the contaminant to be detected and a container wall in which the contaminant is accommodated; selecting two optical pass-bands, one of which is relatively high transmittance level with respect to the contaminant to be detected while the other of which is relatively low transmittance level with respect to the contaminant to be detected; measuring light quantities at the two optical pass-bands when light passes through the bottom and neck of the container; converting the light quantities into respective two electric signals; and comparing one electric signal with respect to one pass-band with the other electric signal with respect to the other pass-band. While the apparatus described by Reich may be suitable to detect one or two predetermined liquid contaminants which may remain in the container, its utility is limited in situations where the possible contaminants are numerous, or the contaminant has been absorbed by the wall of the container. Additionally, the apparatus depends on the transmittance of the contaminant to be detected, and that physical property varies widely depending on the contaminants. This device is typically used to inspect washed glass packages for residual diluted caustic solutions, and not unwashed packages as per the present invention.
U.S. Pat. No. 4,221,961 (Sept. 9, 1980, Peyton) discloses an electro-optic bottle inspector. The device is constructed so that it can detect particles or liquid in a bottle. It has a light source to be disposed under the bottle bottom, a rotative scanner head to be disposed over the bottle neck to receive light passing through the bottle bottom from the light source, and a detector for receiving light reflected by the surface of the scanner head to detect only particulate matters on the bottle bottom. The scanner has reflecting segments and non reflecting portions. The reflecting segments reflect the light passing through the bottle bottom so as to focus a bottle bottom image onto the detector. If there are particulate matters on the bottle bottom, they block the light from the light source to cause a dip in detector output. The non-reflecting portions are provided with an infrared detector for detecting the infrared radiation passing through the bottle bottom. The light to be received by the infrared detector is filtered so that only light having wavelengths in or near one of the absorption bands of liquid to be detected can pass through to reach the infrared detector. If there is liquid in the bottle bottom, the light is partially absorbed to cause a dip in A.C. coupled amplitude of the infrared detector providing an indication of the presence of the liquid. This device is typically used to inspect washed glass returnable bottles for foreign materials that may adhere to the inside of the bottle and could not be removed by the washing device.
U.S. Pat. No. 4,087,184 (May 2, 1978, Knapp, et al.) discloses a method and apparatus for inspecting liquids in transparent containers. The method comprises the steps of illuminating the liquid with a constant intensity light source, imaging the entire illuminated liquid volume, including the meniscus, into a plurality of image planes with fiber optic bundles, and monitoring the fiber optic bundles with an array of constant sensitivity photo transducers. Each photo transducer continually translates the illumination value of the vial image of an assigned and separate unit volume of the liquid-filled container into a voltage signal and each signal is monitored for a signal change indicative of particulate movement. The interfering output signal due to the meniscus decay is corrected, and the accept/reject decision is based upon a composite signal representative of all the differentiated signals received from the array of photo transducers.
U.S. Pat. No. 4,083,691 (Apr. 11, 1978, McCormack, et al.) discloses a method for detecting contaminants in water. The method rapidly detects organic pollutants in water utilizing chemical effervescence to accelerate release of contaminants into the atmosphere above the water sample where they can be detected by conventional air pollution detector tubes. An apparatus for detecting contaminants in the atmosphere above the water solution by detector tube is also disclosed.
U.S. Pat. No. 3,966,332 (June 29, 1976, Knapp et al.) discloses a method and apparatus for inspecting liquids in transparent containers. The apparatus automatically inspects liquid filled containers for particulate contaminants by relative size. The method comprises the steps of illuminating the liquid with a constant intensity light source, dissecting the image of the entire illuminated liquid volume, including the meniscus, with fiber optic bundles and monitoring the fiber optic bundles with an array of constant sensitivity photo sensors. Each photo sensor continually translates the illumination value of an assigned and separate cross sectional unit area of the vial image into a voltage signal and monitors each signal for a signal change indicative of particulate movement. The interfering output signal due to the meniscus decay is corrected, and the accept/reject decision is based upon a composite signal representative of all the differentiated signals received from the array of photo sensors.
U.S. Pat. No. 4,459,023 (July 10, 1984, Reich, et al.) discloses an electro-optic inspection system for transparent or semitransparent containers. The electro-optic inspection system disclosed uses a polarized, scanned optical beam and an array of polaroid optical detectors and a logic signal processing system thereby to securely detect the defects on the transparent or semitransparent containers.
All of the devices describe heretofore have the disadvantage that they depend upon either the presence of particles having a size of at least 5 mm. or the detection of a physical property of a specific liquid contaminant as a means of indicating possible contamination. In the case of contaminated plastic bottles the presence of contaminants may not be manifested with the presence of particles of that size or of any measurable amount of liquid. Rather the contamination would be diffused in the wall of the container and undetectable using the optical methods described in the references. Another difficulty encountered in the possible contamination of plastic containers is that the possible contaminants are numerous and the physical and chemical properties of the contaminants are diverse. Accordingly, a system that is capable of detecting contaminants may not detect other types of contaminants.